The present invention is based on a method for determining the lateral acceleration of a motor vehicle according to the species defined in the main claim. In the known methods, the lateral acceleration is essentially determined from signals of appropriate sensors, e.g. a yaw-rate sensor or acceleration sensor, with the aid of the steering angle and the vehicle velocity. At the same time, the location of the center of gravity of the motor vehicle is estimated from the measured data. In this context, determination of the lateral acceleration and of the location of the center of gravity is used in particular for the control of the vehicle dynamics and for preventing tipping (e.g. vehicle dynamics control VDC, electronic stability program ESP). However, the corresponding devices need additional sensors for determining the lateral acceleration, which create additional costs and can cause disturbances during hard use of a motor vehicle. In this connection, a device is also known from the German Patent 40 03 746 C2 which, for the level control, determines the spring travel of a wheel or an axle having a pneumatic suspension. The sensor supplies a weight-dependent signal which is used for controlling the air pressure in the pneumatic-suspension bellows of the pneumatic suspension. This method permits an axle-load-dependent braking-force metering (ALB).
In contrast, the method of the present invention for determining the lateral acceleration of a motor vehicle having the characterizing features of the main claim has the advantage that the lateral acceleration and the center-of-gravity height are calculated merely, from the signals of a wheel sensor and a load sensor. In principle, further sensors are not necessary.
It is especially advantageous that these sensors are already provided for other functions in many motor vehicles, for example, for controlling the chassis, braking functions, etc. Therefore, further sensors are not necessary, since the signals of the existing sensors can also be used for calculating the lateral acceleration. In this manner, costs are not only reduced, but the functioning of the control units also becomes more reliable, since possible error sources due to additional sensors are eliminated.
The measures specified in the dependent claims permit advantageous further refinements and improvements of the method indicated in the main claim. It is particularly advantageous that the lateral acceleration can be calculated according to a simple formula which is derivable from known parameters such as the axle load, the vehicle mass, the center-of-gravity height and the longitudinal acceleration of the motor vehicle.
Since, in contrast to cornering, no lateral acceleration occurs during straight-ahead driving, the center-of-gravity height can advantageously be determined for this driving condition. Its value is necessary for determining the lateral acceleration.
Furthermore, it is particularly favorable that the signal of the load sensor at one wheel, particularly at a rear wheel, is used for determining the lateral acceleration. Thus, on the basis of the changes in force occurring at the wheel, it is possible to differentiate in a simple manner whether the motor vehicle is traveling straight ahead or in a curve, since the lateral acceleration only has an effect during cornering.
In the steady-state instance, the lateral acceleration can be ascertained from the yaw velocity. This can be measured by a simple sensor, or can be calculated from the wheel speed.
It is further advantageous that the longitudinal acceleration is ascertained by simple time differentiation of the speed signal supplied by the wheel sensor. A resulting torque for the axle-load transfer can advantageously be calculated from the longitudinal acceleration.
The use of a pressure sensor for a pneumatic suspension or a spring-travel sensor for measuring the spring travel has the advantage that these sensors are already built into present-day vehicles, and thus their signals are multiply usable.
A convenient design approach is to determine the center-of-gravity height, particularly during straight-ahead driving, with the aid of a long-term filtering. Short-duration level fluctuations, which can be produced by acceleration changes or road impacts, are advantageously suppressed by the long-term filtering.
It is particularly advantageous that a software program, which is executed accordingly by the control, is used to implement the method.
Should further sensors be present for detecting the lateral acceleration, for example, should a rotation-rate sensor or yaw-rate sensor be present, then they can be advantageously checked and monitored for diagnostic purposes using the method of the present invention. A simple possibility thereby results for checking the existing sensors without additional hardware expenditure. This yields an even greater reliability for the functions implemented in the control unit.